The thing is GUEST,Duh, you don't even need to open the attachments - just clicking on the email to delete it is enough with some of them, if you're working directly through your email program on your computer, rather than using something like MailWasher or the rest.

And the things aren't even restricted to your address book - I had one sent out to people on the mailing list of a previous email that I had been sent, and messed up a number of people's computers, as well as mine. The trouble was I'd recently started using a cable modem, and I hadn't upgraded my security adequately at the time. Cable connections are more vulnerable I understand. (I have better security now, and I hope it's good enough.)